Dry processes involving vacuum evaporation, sputtering, and the like are known as methods for forming a microfabricated circuit pattern on the surface of a thin-film resin substrate. In addition, a subtractive method has been widely used, such method comprising: coating the entire surface of a substrate comprising, for example, a polyimide resin with a metal film comprising, for example, copper foil so as to produce a metal coating material; and removing unnecessary metal film portions by an etching treatment involving photolithography or the like. However, in the case of such subtractive method, it is difficult to form a microfabricated wiring with a width of approximately 30 μm or less. Therefore, further technology innovation has been awaited for the manufacturing of next-generation high-density circuit substrates.
In response to such demand, Patent Document 1 discloses a method for manufacturing metal wiring on a polyimide film. In the method, a chemical that can dissolve polyimide is applied to selected portions on a polyimide film with the use of a lithography apparatus or the like such that selective etching is carried out for recess formation. At such time, remaining polyimide portions on the film surface are modified so as to be able to adsorb metal ions. Subsequently, a metal-ion-containing solution and the polyimide portions come into contact with each other so that metal ions are exclusively adsorbed to the modified portions. Then, a metal-ion-reducing agent is allowed to come into contact with the metal ions such that metal (oxide) nanoparticle assemblies are deposited in polyimide recesses formed by etching described above. At the end, electroless or electrolytic plating treatment is carried out such that a metal film is deposited in each recess, resulting in formation of a microfabricated circuit. The document describes that the method allows low-cost production of a wiring that is microfabricated to a greater extent than that obtained by a conventional subtractive method.
[Patent Document 1] JP Patent Publication (Kokai) No. 2005-29735 A